I wasn't talking about facing tori when the pin is applied: I was talking about facing tori until it is clear the pin will be applied, and you can do nothing about it/have no chance at an opening/escape, I guess.

Graham, I took your question to mean at what point one literally turns one's head away, which I do, say on ikkyo, pretty much when I'm about to hit the mat UNLESS there is enough slack in my (un)controlled arm that it is really easy for me to stay turned towards nage - in which case I don't actively resist at that point, but let my continued slight rotation to nage send a somatic message that something is amiss and he'd better self-correct his extension or he's blown it.

If you mean at what point do I let my center turn away from nage/tori, well, unless I'm working with a real newbie and guiding them through it via my ukemi, I don't let it turn - I may let it BE turned as part of cooperative practice depending on partner's level of training, or I may simply not turn until turned.